Across the electronics manufacturing industry, it is common that ESD (electrostatic discharge) shoes are increasingly being used as one of the practical and effective tools in the combat against the electrostatic discharge damage threat in a typical microchip manufacturing work station. ESD shoe that described in the current invention is referring to any footwear that exhibits an electrical property that falls within the range of 1×10e3 to 1×10e11 ohm as measured according to the ANSI/ESD STM 11.11 (USA).
In such highly competitive and cost-conscious nature of the electronics assembly activities, there also exists a continual need to develop new or better technology that can replace or bring down the cost of an ESD shoes.
There are numerous prior arts that touch and emphasize on the use of shoe grounding device or attachment in the ESD footwear industry and some of them include the followings.
U.S. Pat. No. 4,249,226 highlights an electrically conductive strap that secured to an ordinary shoe to ground static electricity accumulated on the body of a person. However, the L-shaped conductive adhesive strap provide weak adhesion onto the bottom surface of the shoe sole during walking as there is no adequate structural design to hold the tip-end of such L-shaped design.
U.S. Pat. No. 4,812,948 highlights a shoe ground strap with an electrostatic discharge exposed surface and offers protection against static charges building on the wearer and offers protection against electrical hazards if contacting a source of electrical power. However, the “improved” conductive ground strap still clearly inhibits defects. There are loose spaces between the adhesive tape and the side wall of the shoe sole. Such loose space lacks adhesion integrity & become a “defective spot”. Longer use can lead to dust & contaminants accumulation on the exposed adhesive surfaces especially used in wet floor like washroom, toilet, etc resulting in cross-contamination particularly in a cleanroom. Such loose space also promote poor bonding between the electrostatic discharge strap and the bottom surface of the shoes during normal walking or brisk walk especially in some demanding rough floor condition, giving rise to “delamination” of the electrostatic discharge strap, exposing the adhesive surface & can cause direct contamination on the floor of the workplace.
KR2010008914U discloses an electrostatic removal device comprising a U-shape foot wear holder attached to the back of an opening rim of the shoe and a thunderon fiber connecting a ground copper contact and a shoe copper contact. The whole electrostatic removal device is lodged to the back of an opening rim of the shoe, then the ground copper contact 2 is grounded and the shoe copper contact 3 contact the bottom of the shoe.
However, the electrostatic removal device not only exhibit weak fastening capability due to lack of strong structure support at the bottom of the shoe sole, it is also not suitable for use in shoe with rough and uneven bottom shoe sole design.
This gives rise to further research and development on ESD grounding strap used on the shoe with the objective of overcoming those shortcomings as highlighted above and yet able to achieve a favorable cost advantage.